Refractory material



June 6, 1939- J. D. SULLIVAN REFRACTOHY MATERIAL Original Filed Feb. ll,1937 system Bao-sm2 A TTRNEYS.

Patented June l6, 1939 UNITED STATES PATENT OFFICE aamc'roar MATERIALJohn D. Sullivan, Columbus, Ohio, assignor to Battelle MemorialInstitute, Columbus, Ohio, a

' corporation of Ohio 14 calms. (ci. ros-9) My invention relates torefractory material. It has to do, particularly, with the production ofa refractory material which has a high melting point and which ischemically and structurally constituted to withstand the corrosiveaction of slags, gases, metals and other materials at high temperatures.It relates, especially, to the production of a refractory material whichis essentially basic in character.

One of the best basic refractories hitherto available is magnesium oxidewhich is commonly called magnesite. This magnesite usually takes theform of dead-burned magnesite, although electrically sintered magnesiteis sometimes used. Ordinarily, the magnesite is reduced to granular formand then fabricated, either alone or with other materials to formfurnace linings, such as bottoms, walls, ports, et cetera, or to formmagnesite brick, crucibles or other articles.

When magnesite is used for the formation of bottoms of basic open-hearthsteel furnaces, it is ordinarily mixed with a substantial amount of slagwhich bonds the magnesite grains but renders the lining less refractoryand less basic. Also, the

time required for lining a furnace bottom with a composition ofmagnesite and slag is unduly long.

. When magnesite is used in lining the Walls or ports of a furnace, itis customary to provide some sort of binder for the magnesite grains.When clay, sodium silicate, and other materials now commonly used areemployed as binding agents, the resultant product is less refractory,less basic and is more susceptibleto intersticial attack. Sometimes,electrically sintered magnesite grains are mixed with a finely groundwet slurry of the same material which serves as a binder. However, whilea furnace wall structureso formed has a tendency to become extremelyhard on the interior surface thereof owing to the heat of the furnace,the underlyingmaterial being subject to a lesser degree ofv heat has atendency to lose its bond by virtue of dehydration. As a result,

the material disintegrates and the shell-like structure which remains isinadequate for the purposes intended.

' Magnesite brick are ordinarily produced by pressing together grains ofdead-burned magnesite and, usually, by firing such brick at ,elevatedtemperatures. Such brick are basic in nature but they are susceptible,to spalling on rapid temperature changes, and are also vcharacterizedby poor load-bearing capacity at elevated temperatures.

Failure of priorl are magnesite brick often occurs because of thefailure of the bond between the magnesite grains. Frequently, the bondeither melts or loses its strength at too low a temperature or it isattacked by slags, metals or vapors to which it is exposed, with theresult that intersticial penetration of such slags, metals or vaporscauses failure. However, another type of failure arises as a result ofshrinkage of the magnesite grains when the brick are subjected to hightemperatures.

Magnesite grains are usually prepared by deadburning row magnesite whichcomprises subjecting the latter to a temperaturesuicient to decomposethe carbonate, to convert most of the resulting magnesium oxide to thepericlase form, and to effect partial shrinkage of the product. However,the ring is not at high enough temperature or for a sufllcientlyprolonged period to effect complete shrinkage or elimination of porositywithin the graiiis. Consequently, when such brick are subjected inservice to a high temperature on the inner face, and with a temperaturegradient throughout the brick, the hot face tends to shrink excessivelyand to a greater extent than the body, with the result that spalling bypeeling occurs. y

Another disadvantage of prior art magnesite brick is that they areeither extremely fragile before firing or necessitate the use of anextraneous bond that is detrimental'to refractoriness. They are alsoweak between ordinary temperatures and the temperatures at which theyare fired in the kiln.- 'I'his necessitates an expensive method offiring, since the brick cannot be stackedl and must be boxed with silicabrick which bear the load.

lMa'gnesite crucibles are usually made from electrically sinteredmagnesite. One drawback of such cruciblesl is their poor resistance tothermal shock.

If magnesite could be fused completely and satisfactorily fabricatedtoproduce the desired product, a superior refractory would result.Magnesium oxide, because of its high melting point and resistance tocorrosionby basic slags, is an ideal refractory material. However, sincethe melting point of magnesium oxide-is about 2800 degrees C., it is notpuracticable to melt it. In the first place, it can only be melted in anelectric furnace and, when so melted, it reacts with the carbonelectrodes thereof at temperatures much rbelow the melting point of themagnesium oxide to give metallic magnesium and carbon monoxide. 'I'hereaction is more rapid with increasing temperature and is quite vigorousat the melting point of the magnesium oxide. As a result, there is anundue loss of the magnesium-oxide by reduction and vaporization and,even if the magnesium oxide can be melted, the product is quite porousbecause of the blow-holes formed therein.

One meritorious solution of this problem of melting magnesium oxide hasinvolved melting with the magnesium oxide another basic oxide such asbarium oxide, calcium oxide, or both to lower the melting point. It waspossible in this manner to obtain a melting point suniciently low topermit casting.

One of the objects of this invention is to produce a high melting pointrefractory of an essentially basic character and with chemical andstructural characteristics which will be such as to impart to theproduct a longer life than prior art products such as those formed bybonding together grains of dead-burned magnesite or the like.

Another object of this invention is to produce a basic refractory,highly refractory in nature, and with physical and chemical propertiessuperior to those of prior art products.

Another object is to produce such products by the use of comparativelycheap and plentiful materials, and at a comparatively low cost.

Other objects of this invention will appear as this descriptionprogresses.

This application is a division of my application, Serial No. 125,283,filed February ll, 1937, Refractory material, which is a continuation inpart of my co-pending application, Serial No. 753,637, filed November19, 1934, now Patent 2,113,818 issued April 12, 1938, Fused refractoryand method of making the same.

My invention contemplates the use of magnesium oxide as a primaryconstituent of my refractory composition and further contemplates theuse of barium oxide and silica in this composition and playing importantparts therein. The refractory composition in some cases is made byfusion, but in others the step of fusion is not employed. My inventionfurther contemplates the use of my composition for the making ofrefractory products.

Where the step of fusing is to be utilized, the ingredients areproportioned and mixed to yield a product of specified chemicalcomposition. After such preparation, the mass is fused in a furnacecapable of yielding temperatures high enough for this purpose. Forexample, electric furnaces may be used. The use of barium oxide andsilica substantially reduces the melting point; so the loss of magnesiumoxide by reaction with the carbon electrodes of the furnace issubstantially reduced. i

The molten mass may be solidified and, by means well known to the art,reduced to desired sizes and forms for such uses as fabricatingrefractory products, such as furnace linings, brick or other articles.'I'he fused mass may also be cast into molds of predesigned shapes. Thelowering of the melting point permits casting, which is not possiblewhen magnesia alone is used.

When a molten mass of magnesium oxide, barium oxide, and silicasolidifies, the primary material of crystallizationV is periclase. Thatof secondary crystallization is barium silicate. The silica and bariumoxide substantially all unite to form barium silicate unless a largeexcess of silica is present. Likewise, the magnesia crystallizes aspericlase and not as magnesium silicate unless a large excess of silicais present. The

particular silicate of barium 'formed depends on the ratio of BaO toSiO: present. The solidified mass is, therefore, a nucleus of crystalsof perlclase surrounded by and interpenetrated with crystals of bariumsilicate. l

The figure vis a constitutional diagram of the system BaO-S102, and itsuse will facilitate the description of the refractory material of myinvention.

The diagram shows the barium silicate or silicates formed onsolidiiication of a molten mass of barium oxide and silica. For example,a molten mass containing 20 per cent of SiO: and 80 per cent of BaO, onsolidiflcation will comprise a mixture of 2Ba0SiO.` and BaOSiO2 inproportions defined by the lever-arm relationship known to all skilledin interpretation of constitutional diagrams. When a molten mass of MgO,BaO, and SiOz is cooled to permit soliditlcation, MgO crystallizes outrst. The BaO and S102 .act essentially as though no MgO were present.Therefore, the ratio of BaO to SiOz determines the silicate formed. IfSiOz is present in amounts greater than approximately 44 per cent of thesum of the BaO and SiOa, some magnesium silicate may form. Petrographicexamination of a large number of samples showed that, in most cases,magnesium silicates were absent or present in only small amounts, unlessthe SiOs was present in amounts greater than that required to unite withthe barium present to form BaO2SiOz.

For reasons that will appear later, I may want the material of secondarycrystallization, that is, the barium silicate to be highly refractory.To obtain a highly refractory mass I choose a ratio of BaO:SiO2 of highmelting point. The diagram shown in the drawing makes it clear that amixture comprising 80 per cent of barium oxide and 20 per cent of silicais more refractory than one containing 60 per cent of barium oxide and40 per cent of silica. In my invention, I prefer that the molecularratio of BaO to SiO: will not be greater than 2 to 1.

I have discovered that the masses made by this invention, when ground,are cementitious and possess hydraulic properties. I believe that thehydraulic and cementitious properties are due to the barium silicate orsilicates produced in the manner indicated above.

To illustrate the properties of the material made according to that formof my invention involving fusion, I shall give as an example themanufacture of a basic brick. The solidified material is properly sizedand graded. and sufficient water added to temper the material andcondition it physically for fabricating into shape. I may, for example,add the tempering water immediately before fabricating, or I may allowthe tempered mass to remain for a time before fabricating.

On addition of water, the barium silicate exerts its hydraulic effect,and a cementitious bond is formed. The brick so processed, after thecement sets, is strong physically, and can be handled without exercisingundue care. I may use this brick in the unred or unbumed state. If anunfired brick is used in a furnace, the hydraulic bond is converted to aceramic one, at least in the portion subjected to high temperatures. Formany purposes, however, I prefer to burn the brick by methods well knownto the art. I have discovered that the brick possesses excellentstrength from room temperature up to and above that required in firing.In ring, the hydraulic bond is converted to a ceramic one, and the firedbrick possesses excellent physical properties Among the outstandingproperties of brick made according to my invention are refractorly l2,160,924 ness, strength 'under load, especially atelevatedtemperatures, and resistance to slaking by steam. This exampleof a method of making a brick is only illustrative, and other refractoryarticles or products, made by my invention, will inlmany cases, be moreimportant, industrlally. l

In'manufacturing refractory articles from the product made by myrinvention, I may take advantage of the ratio of BaO to SiOz to governshrinkage, or the temperature required to effect a given shrinkage. Ifan article is made from grains of fusedmaterial, it is obvious, ofcourse, that the grains themselves are non-porous. The intersticialspaces between them can' be decreased by subjecting the mass to a highenough temperature to permit either sintering or pyroplastic flow-tooccur.

My observations indicate that vthe amount of shrinkage taking place inmy refractory masses is dependent to a large extent on the quantity ofliquid phase present. Thus in avMgO-BaO-SiO: refractory the MgO is the`most refractory phase.

'v On heating, the rst liquidto form. is silicate.

l 4:1 than ii'it is 3:2.

lIfvI elect to cast the refractory material, I pro- The ratio ofBaOzSiOz governs the melting point of the silicate or `silicatespresent. The diagram of the drawing shows that in the binary system adefinite temperature is necessary to obtain a liquid phase, and that theamount of liquid formed y.at any temperature depends on the BaO:SiO2ratio. The diagram shows, for example, that a higher temperature isrequired to produce any liquid phase if the 'ratio of BaO to SiOz duce aproduct characterized by zero porosity and which is, therefore, Aevenmore resistant to attack by slags andother molten materials.

y I A fabricated refractory made from grains of fused and solidifiedmaterial ishighly desirable because there are no internal voids orporosity .within the grains.

In the caseof rammed linings, brick o1' other articles made from highlyrefractory fused grains,..the only porosity lies in the intersticialspaces between the refractory grains. By judicious grading and` sizing,the totalporosity l furnaces.

can be reduced to a small value. IWhen such linings, brick or otherarticles, so made, are used at elevated temperatures, they arecharacterized' by volume stability, as are the cast products. This is ofparticular value where extremely high temperatures are employedv such asin electric My invention contemplates not only use of fused material,but also takes advantage of the A modied form of my invention,therefore, comprises using grains of magnesium -oxide and bariumsilicate as a bond. I have, for example, added to dead-burned magnesitevarious barium silicates, and pressed or fabricated the mass intoshapes. These masses have been tested in both the fired and unfiredcondition. 'Ihe product so produced is superior inv strength'and otherproperties to similar articles made from dead-burned magnesite alone. Ifound that the green cold crushing strength of a magnesite article wasincreased more than 21/2 times by the addition of 5 per cent of a bariumcement. Similar articles red to 2500 degrees F. showed an increase instrength of approximately 50 per cent.

Another modification of my invention involves mixing raw orunburnedmagneslte, barium oxide, and silica and heating to a hightemperature. In heating, the magnesite is first decomposed to formbarium silicate. of BaO to S1025 that before 'the porous magmagnesiumoxide and carbon dioxide. The latter passes oil.' as a gas, while theresulting magnesiurm oxide is porous in nature. As the tem- Derature isincreased the BaO and SiO: unite to I can sol select the ratio nesiumoxide formed by decomposition vof the raw` magnesite shrinks to theso-called deadburnedcondition a liquid phase of barium silicate ispresent which penetrates into the body of the magnesia. In this way, theinterior'of the mag'- nesia particles become impregnated with bariumsilicate.\ Likewise, the outsides vof theparticles.

become coated. .I re to a predetermined deadburned condition. Theproduct so produced, therefore, simulates that made by fusion andsolidification. It is highly refractory, cementitious in nature, ischaracterized by the grains being coated with and interpenetrated bybarium silicate, and possesses other desirable physical and chemicalproperties. As in the case of fused material, I may govern ringshrinkage of certain bodies bycontrol of the BaOrSiOz ratio. While thevolume stability at high temperatures may not be so good as that`produced by fusion, for many purposes it can be used in place of thefused material, and can be produced ata lower cost.

My invention, therefore, contemplates production of a refractorycomprising magnesium oxide, barium oxide, and silica. It may be made byfusion of the ingredients or by burning, to a high temperature, mixturesof raw magnesite, barium oxide andsilica.. In some instances, I may'evenadd barium silicate or barium oxide and silica to dead-burned magnesite.

BaO-SiOz mass is not critical. I have worked with masses in which thesum of the barium oxide and silica was as muchas 35 per cent of theentire mass. I believe thatbarium silicate should be present at least tothe extent of 5 per cent of the entire mass, although for some purposesas low as 2 per cent may be employed. I prefer in most instances to havethesum of the barium oxide and silica lie between and 20 per cent.

My invention contemplates the use of either pure materials or those ofcommercial purity. It is not necessary to use pure oxides although theymay be used. I may use commercial grades of dead-burnedmagnesite, or Imay use any compound of magnesium which on heating decomposes to theoxide. I may, for example,` use raw magnesite or brucite. I 'may usenatural occurring magnesium silicates such as olivine or serpentine aspart of the raw material charge.

As a source of barium oxide, I may use commercial varieties. In thefusion step, I may use barium carbonate or barium sulphate. Bariumsulphate is sometimes preferred, however, because'oi` its low cost. Inan electric furnace, barium sulphate decomposes and the sulphur iseliminated largely as sulphur dioxide. -As a matter of fact,-IY may useany salt of barium which, under the conditions employed, decomposes toor forms oxide.

In the modification of my invention involving heating of raw magnesite,barium oxide, and

The amount of barium silicate inthe MgO'-y silica, I prefer to add thebarium oxide in thev has given better results than the oxide.. I mayalso use barium sulphate.

For silica, I may use commercial varieties of silica or ganlster. Thisis true for all forms of my invention disclosed herein.

When Lcommercial varieties of the raw materials are used, the productwill inevitably have certain impurities. The existence of theseimpurities will not remove the product from the scope of my invention.In fact, I sometimes find it desirable to add a small amount of aluminumoxide and iron oxide or either of them to the mass, if the raw materialsare low in these ingredients. Use of the usual amount of lime present incommercial magnesites is within the scope of my invention.

4Since MgO-BaO-SiOa is cementitious it may be lground to a fine state ofsubdivision and used to bond lother refractory articles. For example, Ihave successfully added material made by my invention to grainmagnesite, and the resulting product had properties markedly superior tothose of lsimilar products made from grain magnesite alone.

My invention has numerous advantages. It is particularly importantbecause it produces a refractory material for use in lining furnaces.Thus, when used for this purpose the cementitions nature of the fusedgrains of my material eliminates the necessity of using a binder whichis less basic or less refractory. It eliminates the danger prevalentwhere finely ground magnesia is used as a binder because the materialdoes not disintegrate inthe cooler parts of the lining. When used inbottoms of basic openhearth furnaces, addition of slag is unnecessary.Not only is the bottom thus more refractory but the time of installationis decreased.

When used to form brick numerous advantages also result from myrefractory composition. If the brick is to be produced from fused grainsof my material, these grains ,are inherently less porous and lesssubject to shrinkage upon subsequent subjection to high temperatures.Moreover, on the addition of water the cementitious and hydraulic natureof the barium silicate present becomes eiective with the result that thegrains are bound together by the settingl of this cement and the brickare strong physically so that they can be handled without the exerciseof undue care. This facilitates the use of the brick either in the unredor flred state. If the unred brick is used in a furnace, the hydraulicbond is converted to a ceramic bond in those portions thereof which aresubjected to high temperature.

Where my refractory material is produced by mixing raw or unburnedmagnesite, barium oxide, and silica and heating to a high temperature,in the manner described above, the impregnation of the magnesiaparticles and the coating thereof -with the barium silicate results in aproduct which, in qualities, closely approximates that made by fusionand solldication. It is highly refractory, cementitious in nature andpossesses other desirable physical and chemical properties. Likewise, itis comparatively low in cost.

Various other advantages will appear from the above description and theappended claims.

In the claims, the terms barium oxide or magnesium oxide are to beinterpreted in their broad sense and include those salts of barium ormagnesium which, under the condition employed, decompose to or form theoxide.

Having thus described my invention, what I claim is:

1. The method of making a refractory material which comprises mixing rawmagnesite, barium oxide and silica in such proportions that onsubsequent heating the resulting product wil be characterized by havingmagnesium oxide as its principal constituent, and heating to effectdecomposition of the magnesite, combination of the barium oxide andsilica followed by deadburning of the magnesia.

2. 'I'he method of making a refractory material which comprises mixingraw magnesite, barium oxide and silica in such proportions that onsubsequent heating the resulting product will contain from 2 to 35 percent of barium oxide and silica, and heating to eifect decomposition ofthe magnesite, combination of the barium oxide andi silica followed bydead-burning of the mag- !ieS a.

3. The method of making a refractory material which comprises mixing rawmagnesite, silica and a member selected from the group consisting ofbarium carbonate and barium sulphate in such proportions that onsubsequent heating the reg sulting product will contain from 2 to 35 percent of barium oxide and silica, and heating to effect decomposition ofthe magnesite and barium carbonate or barium sulphate, combination ofthe silica and barium oxide formed by decomposition of the bariumcarbonate or barium sulphate and followedby dead-burning of themagnesia.

4. The method of making a refractory material whih comprises mixing rawmagnesite, barium oxide and silica in such proportions that onsubsequent heating the resulting product will contain from 2 to 35 percent of barium oxide and silica with a molecular ratio of the bariumoxide to silica of not more than 2 to 1. and heating to effectdecomposition of the magnesite, combination of the barium oxide andsilica followed by dead-burning of the magnesia.

5. The method of making a refractory material in which magnesium oxideis the chief con- ,stituent and barium oxide and silica are minorconstituents, which comprises mixing raw magnesite, barium oxide andsilica, with the barium oxide and silica in such proportions that byapplication of heat barium'silicate forms and assumes a state offluidity permitting it to penetrate the magnesium oxide resulting fromdecomposition of magnesite before the latter shrinks to a dead-burnedcondition, and heating to effect decomposition of the magnesite,combination of the barium oxide and silica, followed by deadburning ofthe magnesia.

6. The method of making a refractory material which comprises mixing rawmagnesite, barium oxide and silica with the raw magnesite as the chiefconstituent and with the barium oxide and silica in such proportionsthat by application of heat barium silicate forms in an amount of from 2to 35 per cent of the entire mass and assumes a state of fluiditypermitting it to penetrate the magnesium oxide resulting fromdecomposition of the magnesite before the latter shrinks to adead-burned condition, and heating to effect decomposition of themagnesite, combination of the barium oxide and silica, followed bydead-burning of the magnesia.

7. The method of making a refractory material which comprises mixing rawmagnesite, barium oxide, silica. and a member selected from the groupconsisting of iron oxide and aluminum oxide,v in such proportions thaton subsequent heating the resulting produce will be characterized byhaving magnesium oxide as its principal constituent and will containfrom 2 to 35 per cent of barium oxide and silica, and heating to effectdecomposition of the magnesite, combination. of the barium oxide andsilica followed by dead-burning of the magnesia.

8. The method of making a refractory material which comprises mixingmagnesium oxide,

^ barium oxide and silica, the sum of the barium oxide and silicaranging from 2 to 35 per cent of the entire mass, and heating to effectcombination of the barium oxide and silica.

9. TheA method of making a refractory material which comprises mixingmagnesium oxide,

barium oxide and silica, the sum of the barium oxide and silica rangingfrom 2 to 35 per cent of the entire mass with a molecular ratio of thebarium oxide to silica of not more than 2 to 1,`

20 subsequent heating the resulting product will contain from 5 to 3 5per cent of barium oxide and silica, and heating to effect decompositionof the magnesite, combination of the barium oxide and silica followed bydead-burning of the mag- 25 nesia.

11. 'I'he method of making a refractory material which comprises mixingraw magnesite, barium oxide and silica in such proportions that onsubsequent heating the resulting product will contain from 10 to 25 percent of barium oxide and silica, and heating to eileot decomposition ofthe magnesite, combination of the barium oxide and silica fol1owed bydead-burning of the magnesia.

12. The method of making a refractory material which comprises mixingraw magnesite, barium oxide and silica in such proportions that onsubsequent heating the resulting product will be characterized by havingmagnesium oxide as its principal ingredient and heating to ciectdecomposition of the magnesite and chemical union of the barium oxideand silica.

13. The method of making a refractory material comprising magnesia andbarium silicate in which magnesia is the principal ingredient whichcomprises mixing magnesite, barium oxide and silica and heating.

14. The method of making a refractory material in which magnesium oxideis the principal ingredient which comprises mixing magnesite and bariumsilicate. and heating.

i JOI-1N D. SULLIVAN.

